Although three-dimensional imaging has been around for quite some time, recent advances in computing technology have made it more practical to create "single image stereograms." Single Image Stereograms (SISs for short) create the illusion of depth through a technique known as free-viewing. They do not require any special glasses or other equipment to view the 3-D effect.

The first SISs consisted of random dots and were known as Single Image Random Dot Stereograms (SIRDS.) As techniques in the creation of SISs were refined, it became possible to control the "pattern" image enough to hide a three-dimensional image within a two-dimensional image that could be viewed normally. The images need no longer consist of "random dots."

SISs have gained popularity as posters, postcards, and books in shopping malls around the globe. They have also turned up in a number of periodicals, both as entertainment and as advertisement. It is now possible to have custom stereograms made for promotional or other applications at a very reasonable cost.

Free-viewing

In order to see the three-dimensional image within a SIS, the eyes must be aligned as they would be if one were looking at an image with the actual depth represented in the SIS. As it is normal for us to align our eyes to focus on a flat image at it's actual position in space, it generally requires some practice to be able to free-view SISs.

There are two techniques for free-viewing SISs: parallel and cross-eyed. Either technique may be used to view most images. However, each stereogram is designed specifically for one of the techniques. If the image is viewed using the other technique, the image will, in most cases, have reversed depth. That is, it will look as if the three-dimensional scene has been turned inside-out. Most SISs are designed for parallel viewing.

Here are some general free-viewing tips:

• Either technique may require quite a bit of initial effort however, viewing SISs generally becomes easier with each subsequent attempt and each new image.

• Some images are more difficult to view than others.

• The three-dimensional illusion often appears suddenly.

• There is no evidence that free-viewing has any ill effect on the eyes or vision. However, free-viewing is not something you normally do. It exercises the eye muscles in a different way from normal viewing. As with any exercise, it is possible to overdo it. If you develop a headache or temporarily blurred vision, you are overdoing it. Remember to take frequent breaks while learning to free-view.

Parallel Viewing

In parallel free-viewing, the eyes are diverged as they would normally be if looking at an object twice as far away as the SIS. There are a number of tricks to help one accomplish this minor feat:

• Allow the eyes to lose their focus on the SIS and stare at the SIS as if staring into space. As the three-dimensional illusion begins to appear, it will become easier to focus on the image.

• Try staring at a distant object and slowly shift your gaze to the SIS without changing the position or focus of your eyes.

• If viewing a printed SIS, stare at a distant object and insert the SIS image directly in front of the eyes, again, without changing focus. Move the image slowly away from you until the three-dimensional illusion appears.

• Many SISs have "alignment dots" at the top or bottom. Diverge the eyes so that there appear to be three dots. Shifting your gaze to the image without changing focus should make the three-dimensional effect visible.

• Placing a SIS behind a piece of glass sometimes makes it easier to view. Try staring at your own reflection in the glass. This will cause the eyes to diverge, making the three-dimensional effect visible.

Cross-Eyed Viewing

The cross-eyed technique requires a slightly different approach:

• Hold up a finger or a pen between you and the SIS. Look at the tip of the object. Adjust the distance between you and the SIS and the position of the pen in-between until the three-dimensional effect appears.

Custom Stereograms

Evermore Enterprises can produce custom stereograms (including Single Image Stereograms) for promotional or other use by your organization. Please direct inquiries to: